1986 Nissan 720 blown head gasket

[NISSAN_720Crawler]

Hey guys, my 1986 nissan 720 blew a headgasket and im wondering what i need to know to fix it. i have the gasket already and am going to fix it with my friend soon. Torque settings for head bolts? shortcuts for getting passed the timing gear?

[datzenmike]

Do not unbolt the cam sprocket without finding out how to prevent the timing chain tensioner from falling out!!!!!!!!!!!!!!!

 

You need to physically block it or it will fall out and add 6 hours of extra work to fix it.

 

 

 

 

If this happens you are screwed...

[Jesse C.]

Get a service manual or download torque specs of the internet. 

 

And what Mike said ^^^^^^

[HRH]

If it's bad, expect to take the head to a machine shop and have welding done.  It tends to eat a hole in between 3 and 4 if you blew it and ran it for a bit.  Look for a trough forged out by exhaust gasses swapping.

[datzenmike]

Disconnect battery

Drain coolant at least half way. Remove upper rad hose from intake. Disconnect heater return hose to bottom of intake. Unplug temp gauge wire, throttle cable, carb wiring, vacuum lines (qty.1) to vacuum advance, (qty. 2) charcoal canister. Battery ground strap on intake. Remove distributor cap and wires. Disconnect the exhaust down pipe from end of exhaust manifold, disconnect the hose from the PCF valve beside below the carb.   Remove valve cover. *

 

Loosen cam sprocket LOOSEN ONLY.

Set engine to TDC compression stroke on #1 cylinder.

Set timing tensioner block in place.

Set hand brake or block rear wheels and take out of gear.

Mark cam sprocket and timing chain so they go back together in same orientation.

 

*Probably missed a few but the idea is to leave the intake and carb and the exhaust manifold and EGR tube all together on the head rather than breaking bolts off or damaging the EGR tube which is rusted on anyway.... and lift the head away complete. If the head needs work it's much easier to remove these things when the head is off and you can get at them. It will be awkward to lift off, more than heavy, so get help when the time comes. When cleaning the under side of the head tilt up only enough to get at it or remove the carb first so sediment doesn't get stirred up.

 

Clean head surface but plug cylinders 2&3 to keep crap out.

Clean head bolt holes thoroughly.

Be sure to find and save the two alignment dowels that mate the head to the block. They look like 1/2" sections of 1/2" copper pipe. These need to go back into the head or block to locate/align the head when putting back on.

Clean the head surface but have a care, it's aluminum and soft.

Clean both surfaces so clean you wouldn't mind eating off them.

Inspect the area where the gasket blew. Seldom is it warped as the Z24 is well known for gasket failure from failure to re-torque the head bolts every year. If you can check for flatness with straight edge. If you can get a 0.003" feeler gauge under the edge it should be plained. If you send it out to be checked you may as well just say plain it as they will say it needs it weather it does or not.

 

Install head gasket dry, never with gasket cement, goo or sealers slipping it over the alignment dowels and lower head onto it.

Clean an re-use the head bolts,replacing only those that might be damaged. They are completely re-usable. Oil the threads.

Torque to 20 ft lbs using this pattern...

 

R A D

8.....7

4.....3

2.....1

6.....5

10...9

 

Using the same pattern torque to 40 ft lbs.

 

Using the same pattern finish torque to 60 ft lbs.

 

Replace cam sprocket and chain in proper order. The rest is basically the reverse of removal. You do not need to re-torque the head but if you do... do it on an absolutely cold engine. Loosen one bolt and tighten to 60 ft lbs. Then the next. One bolt loose at a time. Any order. Next year re-torque the head the same way and every year after and the gasket will never blow.

[HayesK]

On 2/19/2016 at 10:16 PM, datzenmike said:

Loosen cam sprocket LOOSEN ONLY.

Set engine to TDC compression stroke on #1 cylinder.

Set timing tensioner block in place.

Set hand brake or block rear wheels and take out of gear.

Mark cam sprocket and timing chain so they go back together in same orientation.

I am attempting to replace the head gasket on my 85 and I feel quite comfortable with being able to remove the parts and keep them labeled and in order and whatnot but I am self-taught and I am having trouble understanding what exactly this paragraph means. 

Loosen only because of what you said earlier? to protect the timing chain from falling out?

What is a timing tensioner block

Physically mark them with a sharpie? anywhere on the chain and sprocket or just the tip? 

Any advice would also be appreciated.

Thanks,

Hayes